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Home Q & A Board Biology-Related Homework Help Anatomy and Physiology
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ns7 ns7
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11 years ago
I'm curious why arteries or arterioles don't have it, but capillaries do.
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11 years ago
the cappilary wall has one layer endothelium so thin that gas and molecules such as oxygen, water,protein and lipid can pass through them driven by osmotic and hydrostatic pressure.
capillaries do'nt have smooth muscle likes artries on arteriols so its size is passive not contract or dilate. but they realese substance like endothelin (for contraction) and nitric oxide (for dilatation) act on near by smooth muscle cells in the walls of near by vessels.
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